Insulators are commonly used for supporting high voltage transmission lines and other components and keeping such components in spaced relationship with respect to other supporting structures such as transmission line towers, housings, and the like which are normally at or very near ground potential. A typical example of an insulator of this general type is shown in U.S. Pat. No. 3,898,372, Kalb. Modern insulators of this type generally include a central rod of an insulating material such as fiberglass, the ends of the rod being firmly attached to end members which are normally electrically conductive. The rod and the end members comprise the primary load bearing structure, the rod being very strong and the end members being crimped or otherwise fixedly attached to the rod ends. The rod is usually surrounded by a series of skirted members called "weathersheds" or simply "sheds" which are made of a good insulating material, originally ceramic but more recently a rubber-like polymeric material such as EPM. The sheds are placed end-to-end along the rod to form a very long external surface path between the conductive end members, the length of the rod and the number of sheds being chosen in accordance with the voltage conditions in a manner which is conventional. Finally, a dielectric material is used to fill the spaces between the weather sheds and the central strength member to prevent the ingress of dirt and moisture which might form a conductive path. A material such as a silicone grease is suitable for this purpose.
In use, such insulators are mounted with the end members connected to the points between which there is, or is expected to be, a high potential difference. The insulator can be used as a hanger, supporting a transmission line with the insulator being suspended between an arm of a tower and the transmission line, or the insulator can be used as a standing member supported on a housing with the high voltage component at the upper end.